This invention relates to the modification of a surface and more specifically to enhancing the wettability character of a surface by depositing thereon a coating comprising a hydrophilic layer of plasma-deposited polar organic compound. Still more particularly the invention relates to a method for modifying and improving the wettability of inorganic substrates by plasma deposition of a coating comprising a first layer of non-polar organic compound and a top layer of polar organic compound, and to coated articles prepared by the processes of this invention.
Methods for the deposition of polymeric films upon a substrate by employing a plasma generated by an electrical discharge in an atmosphere of gaseous organic monomer are well known in the art. For example, in U.S. Pat. Nos. 3,318,790 and 3,421,930, the problems attaching to such polymerizations initiated by corona discharge are discussed and methods for producing polymeric coatings are disclosed. Modifying surfaces by cold plasma deposition of fluorocarbon monomers to alter the surface characteristics of substrates is described in U.S. Pat. No. 4,188,426, and bonding of hydrophilic polymeric coatings to hydrophobic contact lens materials is disclosed in U.S. Pat. No. 4,143,949. In general, these processes have been successful in achieving modification of surface characteristics, and particularly where hydrophobic coatings on metallic substrates are desired. The application of non-polar coatings such as fluorocarbon polymer films by these processes to inorganic substrates including metallic substrates to achieve improved lubricity, a high degree of hydrophobicity and chemical inertness has been widely described and used in the coating art. Where increased hydrophilicity is desired, particularly for inorganic substrates, the deposition of durable, well-adhered coatings has been less successful.
The development of a method for depositing thin, pin-hole free hydrophilic coatings on inorganic and particularly on metallic substrates that adhere well and are durable under a variety of end use conditions would thus be a useful advance in the coating art.